Here is something that the rule book says nothing about!

[quincy]

Growing up we had a really good pitcher that could throw righty or lefty. He never jumped back and forth but he did pitch a ton of innings.

 

[MTR]

I revoke my Busch Light offer. It was the PU's ruling I remember, because he forced the batter to bat from the right handed batter's box. It looks as though MLB created a rule afterwards that forced the pitcher to declare which hand they were intending to pitch with.

That's okay, I only drink beer.